Inosculation is a natural phenomenon in which trunks, branches, or roots of two trees grow together. This event usually occurs between trees of the same species but can also happen between trees of different species.
In the first photo to the right, you can see what looks like a clump of oak trees. This photo shows two limbs or trunks of this cluster fusing together. There are many examples out at the arboretum where there are multiple trunks of an oak tree that are joined at the base. I haven’t been walking around the arboretum over the past hundred years to watch all of these trees grow, but I imagine that a small cache of acorns sprouted, grew up together, and literally grew together.
In the next three photos, there is an example of two different species. I have walked past this Oregon oak tree and Douglas-fir many times. The other day I noticed that they appear to have grown together at the base. They look to be about the same size so they probably sprouted at the same time. This pair is just past the barn on the left. The Douglas-fir winds up through the canopy of the oak tree and has an interesting wavy trunk. Both of their canopies lovingly intertwine with each other.
The word inosculation is derived from the Latin word osculum, which translates as “to kiss.” I recommend reading the biology behind how inosculation works. In a nutshell, it is about the bark layers coming in contact with each other, especially the cambium layer which is the tissue responsible for growth. The bark layers wear away and can come in contact with each other as they slightly rub together from the movement of the wind. My understanding is that it also happens through the pressure of trees growing into each other as they expand. The two touching parts can be two branches, two trunks, or a branch to a trunk. It can happen between roots too. To me, it essentially sounds like grafting trees together which is done all the time with fruit trees.
